This invention relates in general to gloss and density control for fused marking particle images produced by electrographic reproduction apparatus, and more particularly to gloss and density control of electrographic reproduction apparatus marking particle images fused to a substrate, such control being based on gloss/density parameters determined by an on-line gloss/density meter and fed back to the reproduction apparatus logic and control unit.
In electrographically reproducing information on substrates (commonly referred to as receiver members), a suitable colorant is laid down on a receiver member, in an image-wise pattern, and then permanently fixed to the receiver member. The colorant is generally, for example, a colored ink or a set of pigmented marking particles. After the image is fixed to the receiver member, it exhibits a distinctive reflection characteristic commonly referred to as gloss. The plain surface of the receiver member itself also exhibits a unique gloss. In order to maximize the acceptability of the electrographic reproductions, control of the gloss of the marking particle image is desirable. For example, at times it is desirable to match the gloss of the marking particle image to the gloss of the receiver member.
There are three prominent standards that describe the measurement of gloss: The German DIN 67530, the International ISO/DIS 2813/8254, and ASTM D 523. From the experimental setup, they differ slightly, but essentially, they are based on a few fundamental principles. Gloss by definition is measured in reflection geometry. When a sample is very smooth and reflects well (which is equivalent to high gloss) most reflected light is contained within the direct specular beam while only a small part of the intensity is reflected as a diffused light. The ratio of specular to diffuse light varies with the gloss. When most light is reflected diffusely, the sample is perceived as low gloss (matte).
Most commercially available gloss meters, in determining gloss, reflect light from a marking particle image bearing receiver member, and measure the diffuse component of the reflected light by blocking the specular component of such reflected light. To obtain a sufficient signal-to-noise ratio for suitable effective gloss meter measurement, such gloss meters often employ the bright white illumination provided by a Xenon flash lamp. The resulting measurement can then be quite accurate, but is relatively slow, with cycle times measured in seconds.
Typically, the suitable standard for measuring gloss is described as directing a light beam at a sample (substrate), blocking the specular beam and only detecting the diffused light around it with a conventional light sensor. While this setup provides an excellent dynamic range, it has proven to lead to a very high sensitivity of the signal to the position of the sample relative to the sensor (i.e., if the distance to the sample varies just slightly from a preselected distance, part of the specular beam is unblocked and detected in addition to the diffused light). The accuracy required by such a standard is clearly extremely difficult to obtain, and has previously only been achievable with a table-top (off-line) sensor.
In view of the above, it is the purpose of this invention to provide for gloss/density measurements of a marking particle image produced on a receiver member in an electrographic reproduction apparatus, on line, such that meaningful feedback for the reproduction apparatus can be obtained to control gloss/density of the reproduced image. The on-line gloss/density meter includes at least one light emitter for emitting a collimated light beam, the emitter mounted in operative association with the transport path, preferably substantially immediately downstream, in the direction of receiver member travel, from the fuser assembly. At least one light collector, mounted in operative association with the at least one light emitter and the transport path detects light from the at least one emitter, reflected from a receiver member transported along the transport path, and produces a signal corresponding to such reflected light. A guide element is associated with the transport path and directs a receiver member into a predetermined specified location relative to the beam of light from the at least one emitter to reflect light toward the at least one collector. A logic and control unit controlling operative parameters of the electrostatographic reproduction apparatus, responsive to signals from the at least one collector, precisely controls operating parameters for the electrostatographic reproduction apparatus to control gloss and/or density.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.